Method for control of fluid loss and gas migration in well cementing

ABSTRACT

This invention discloses a polymer composition, a cement slurry containing said polymer composition and a method of using the cement slurry to cement a borehole penetrating a subsurface earth formation wherein the polymer composition is made by polymerizing a vinylamide morpholine derivative with a styrene sulfonic acid salt in the presence of a humate. The polymer composition operates to reduce fluid loss from the cement slurry to the subsurface formation.

This is a continuation-in-part of application Ser. No. 09/092,294 filedJun. 5, 1998, which is a continuation-in-part of application Ser. No.08/964,622 filed Nov. 5, 1997, now U.S. Pat. No. 5,988,279.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention broadly relates to a method of cementing wells whichpenetrate subterranean formations with a slurry of hydraulic cement inwater. The invention further relates to an improved composition for usein well cementing, whereby loss of fluid from the slurry is reduced andmovement of gas into the slurry from a subterranean formation adjacentthe slurry is substantially reduced, if not eliminated. The inventionstill further relates to an improved method of making the improvedcomposition.

2. Related Art and Problem Solved

It is known in the art of well cementing to form a sheath of hardenedcement in the annular space between a well pipe, such as a casing, andthe walls of a wellbore which penetrates a subterranean formationwherein the purpose of the sheath is to support the casing in thewellbore and to prevent the undesirable movement of formation fluids,i.e., oil, gas and water, within the annular space between subsurfaceformations and/or to the surface of the earth. The process of formingthe sheath is referred to in the art as primary cementing.

Thus, in the art of primary cementing, a slurry of hydraulic cement inwater is made, the slurry is pumped down the casing and circulated upfrom the bottom thereof in the annulus to a desired location therein andthen permitted to remain undisturbed--static--in the annulus for a timesufficient to enable the hydraulic cement to react with the water in theslurry, i.e., to set, to thereby produce the sheath of hardened cement.

The slurry of cement, when first placed in the annulus, acts as a trueliquid and will, therefore, transmit hydrostatic pressure. Thus,sufficient hydrostatic pressure is exerted, as an element of the processof primary cementing, to balance the pressure of any gas in theformation to prevent the movement of gas from the formation into andthrough the slurry in the annulus. Movement of gas from a formation intoand through a cement slurry in an annulus is referred to in the art asgas migration.

Gas migration can result in movement of gas in the slurry from oneformation to another or even to the surface of the earth. Such movementcan cause loss of control of pressure and result in a blowout. Asmentioned previously, gas migration can be controlled if sufficientpressure can be transmitted through the slurry. However, loss of controlcan be experienced and gas migration can occur if the slurry does notpossess the properties of a true liquid and is unable to transmithydrostatic pressure.

Before a slurry of hydraulic cement sets into a hardened mass havingcompressive strength, events take place which cause the slurry to losethe ability to transmit hydrostatic pressure. One of the events is theloss of liquid from the slurry to the formation. Another event is thedevelopment of static gel strength in the slurry.

It is clear that the loss of water from a slurry of hydraulic cementemployed in a well cementing operation will diminish the ability of theslurry to transmit hydrostatic pressure. The ability to control waterloss becomes more difficult as the temperature increases, especially attemperatures greater than about 200 degrees F. It is, thus, an object ofthis invention to provide an improved composition for use in wellcementing, whereby water loss from a slurry of hydraulic cementcontaining the improved composition is reduced at temperatures up to andgreater than about 200 degrees F. It is a still further object of thisinvention to provide an improved method of making the improvedcomposition.

When a slurry of hydraulic cement becomes static it begins to develop aproperty known in the art as static gel strength, or simply gelstrength. (In this regard, note Sabins, et al., "The Relationship ofThickening Time, Gel Strength, and Compressive Strength of Oil wellCements," SPE Production Engineering, March 1986, pages 143-152.)

Gel strength is not compressive strength. Thus, as a slurry of hydrauliccement sets into a hardened mass having compressive strength, it isbelieved that the hardening process experiences phases which arerelevant to the phenomenon of gas migration. (See Eoff et al, U.S. Pat.No. 5,339,903.) In the first phase of the process, it is believed thatthe slurry contains sufficient liquid to enable the slurry to possessthe characteristics of a true liquid. Accordingly, during the firstphase, the slurry can transmit hydrostatic pressure and gas migrationcan be prevented by applying sufficient hydrostatic pressure which istransmitted against a gas-containing formation to thereby prevent themovement of gas from the formation into the slurry.

During the first phase of the process, some of the liquid in the slurryis lost--this is referred to as fluid loss--and the slurry begins tostiffen due to the formation of a gel structure. During this firstphase, even though fluid loss and gel formation do occur, it is believedthat the setting cement retains the ability to transmit hydrostaticpressure. Accordingly, gas migration can be prevented so long as theslurry exhibits the properties of a true liquid and so long as thestiffness of the gel structure--referred to as gel strength--is lessthan or equal to a certain value which has been referred to in the artas the first critical value. The first critical value is believed to beabout 100 lb_(F) /100 sq.ft.

In the second phase of the hardening process, the gel strength of theslurry exceeds the first critical value and continues to increase andfluid loss may continue, although at a rate much lower than thatexperienced in the first phase. During the second phase, it is believedthat the setting cement loses the ability to transmit full hydrostaticpressure. Accordingly, gas migration may not be prevented during thesecond phase because the gel strength of the slurry may be too high topermit full transmission of hydrostatic pressure, but too low to resistpressure exerted by gas in the formation against the slurry. Thiscondition exists until the gel strength increases to a value, referredto in the art as the second critical value, which is high enough toresist pressure exerted by gas in the formation against the slurry. Thesecond critical value is believed to be about 500 lb_(F) /100 sq.ft.

In the third phase of the hardening process, gas migration is preventedbecause gel strength is equal to or greater than the second criticalvalue. The cement continues to harden until it attains a compressivestrength deemed sufficiently high to enable further operations in thewellbore.

It is noted that Sabins, et al., mentioned above, provide a discussionand a description of a method and apparatus to experimentally determinegel strength value.

In view of the above, in order to minimize gas migration, it isdesirable that maximum fluid loss, if any, should occur prior to thebeginning of the second phase of the cement hardening process; that thefirst phase should continue over an extended period of time; and thatthe second phase should be completed in a short period of time.

The period of time required for a slurry of hydraulic cement to attainthe first critical value from the time the slurry becomes static hasbeen defined in the art as "Zero Gel Time," and the period of timerequired for a slurry to attain the second critical value from the timeit attains the first critical value has been defined in the art as"Transition Time."

It is, thus, another object of this invention to provide a compositionfor and a method of extending Zero Gel Time of a slurry for a timesufficient to enable the rate of fluid loss from the slurry to declineto a substantially constant value and to shorten Transition Time.

It is a further object of this invention to provide a method ofcementing a wellbore which penetrates a gas-containing subterraneanformation, whereby gas migration at temperatures up to 400° F. andparticularly above 200° F. is reduced if not eliminated.

It is still another object of this invention to provide an improvedprocess of making the composition of this invention, whereby the productof the improved process operates to enhance the results obtained whenusing the product of the improved process to reduce fluid loss from aslurry of hydraulic cement.

It is yet another object of this invention to provide the product of theimproved process.

A cement having an extended Zero Gel Time, the provision of which is astated object of this invention, is referred to herein as a "low gelstrength cement." It is believed, in addition to the use in primarycementing as described above, that a low gel strength cement findsparticular use in remedial cementing practices such as in placementthereof by coil tubing and by dump bailer.

SUMMARY OF THE INVENTION

It has now been discovered that the random copolymerization of avinylamide morpholine derivative with a styrene sulfonic acid salt, whenperformed in the presence of a humate, provides a polymer compositionwhich, when added to a slurry of hydraulic cement made with either freshor salt water, and more particularly salt water, is effective to reducefluid loss from and modify the gel strength of the slurry. It isbelieved that the polymer composition can effectively modify the fluidloss from and gel strength of a slurry of hydraulic cement attemperatures of up to about 400° F. The fluid loss control and gelstrength modification properties of the polymer composition render thecomposition very useful in a method of cementing a wellbore whichpenetrates a subterranean gas-containing formation whereby migration ofgas from the formation into and through the slurry in the wellbore isreduced.

The vinylamide morpholine derivatives useful herein are selected fromcompounds represented by the general formula ##STR1##

The polymerizable styrene sulfonic acid salts useful herein are selectedfrom compounds represented by the general formula: ##STR2## wherein R₃is --H and M is --Na, --K, --NH₄, or --Ca1/2.

The material referred to above as a "humate" is a generalization for anynaturally occurring derivative of humic acid. Humic acids areallomelanins found in soils, coals and peat, resulting from thedecomposition of organic matter, particularly dead plants, and consistof a mixture of complex macromolecules having a polymeric phenolicstructure.

A humate useful herein, available from American Colloid Company underthe trademark ENERSOL SC, is described as comprising a long chain,highly substituted, molecular structure derived from humic acids whoseactive ingredients are potassium humate and humic acid. ENERSOL SChumate is substantially (95-100%) water soluble and is known as a plantnutrient activator.

The polymer composition of this invention is, thus, a random copolymerwhich is comprised of the product of the process of reacting, in thepresence of a humate, a monomer selected from compounds within the scopeof formula (1), the vinylamide morpholine derivative, with at least onemonomer selected from compounds within the scope of formula (2), thestyrene sulfonic acid salt.

The polymerization reaction can also include other acrylic derivatives.

The polymer composition of this invention is sometimes referred toherein as the gel strength modifier/fluid loss additive of thisinvention.

The improved method of this invention for making the polymercomposition, in broad terms, comprises: first, forming an aqueousmonomer solution comprising a first monomer selected from a vinylmorpholine derivative, as defined, at least one second monomer selectedfrom a styrene sulfonic acid salt derivative, as defined, and a humate;second, adjusting the temperature and pH of the monomer solution in thepresence of a water soluble chain transfer agent; and, third, causingreaction to begin with a suitable initiator material.

The polymer composition of this invention, and the method of preparationthereof, should be distinguished from the method of making graftpolymers and the resulting product. In this regard, grafting polymers ona natural product backbone is a known process. An example of the processis found in Fry, et al., U.S. Pat. No. 4,703,801 and Fry, et al. U.S.Pat. No. 4,676,317 each of which discloses a natural product backbone,lignin or lignite, having grafted thereto polymers includinghomopolymers and copolymers of 2-acrylamido-2-methylpropanesulfonic acidand N,N-dimethylacrylamide. The Fry, et al., polymer graft is disclosedto be useful in a cementing composition as a fluid loss additive. Fry,et al., do not mention modification of slurry gel properties, zero geltime, transition time or gas migration.

Eoff et al., U.S. Pat. No. 5,339,903, disclose grafting polymer groupsto tannin, a natural product backbone, wherein the polymer groupsconsist of at least two, and preferably three, vinylamide derivatives.Eoff et al. do mention modification of slurry gel properties, zero geltime, transition time and gas migration.

Another example of the use of a polymer grafted natural product backbonein a well cementing composition is provided in Huddleston, et al., U.S.Pat. No. 5,134,215 and Huddleston, et al., U.S. Pat. No. 5,147,964.Huddleston, et al., each discloses a wattle tannin backbone grafted with2-acrylamido-2-methylpropanesulfonic acid or with2-acrylamido-2-methylpropanesulfonic acid and acrylamide. Huddleston, etal., disclose their polymer-grafted tannin to be useful as a fluid lossadditive in a cementing composition, but they do not mentionmodification of slurry gel properties, zero gel time, transition time orgas migration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By this invention there is, thus, provided a process for making apolymer composition, the product of the process (referred to herein asthe polymer composition), a hydraulic cement slurry compositioncontaining the polymer composition and a method of using the hydrauliccement slurry composition to cement a pipe, such as a casing, in awellbore, whereby fluid loss is reduced and gas migration in the cementslurry is eliminated, or at least substantially reduced.

Accordingly, the use in primary cementing of a hydraulic cement slurrycomposition containing the polymer composition, wherein conventionalcement slurry placement techniques are employed to secure a pipe in awellbore, results in low fluid loss from the slurry and eliminates, orat least substantially reduces, gas migration, i.e., the movement ofgas, from the formation into and through the slurry.

As mentioned, gas migration is a problem to be avoided because it leadsto communication by way of the well annulus between formations and/or tothe surface and is, thus, a source of surface and subsurface blowouts.

Gas moving in a hardening cement slurry can create permanent channels inthe set cement. The gas channels must be filled with cement in aseparate remedial cementing technique called "squeezing" in order toprevent the communication mentioned above.

Gas migration is caused by the inability of the cement slurry placed inthe zone adjacent the gas-containing formation to resist the pressure ofthe gas in the formation. Accordingly, the gas moves from the formationinto and through the slurry.

The hydraulic cement slurry composition of this invention is formulatedto provide a Zero Gel Time of greater than about one hour and aTransition Time of less than about one hour, whereby the time in whichthe hardening cement slurry can transmit hydrostatic pressure ismaximized, and the time in which gas migration can occur is minimized.Furthermore, fluid loss from the hydraulic cement slurry composition ofthis invention is less than about 100 cc/30 minutes and maximum fluidloss is believed to occur during the Zero Gel Time period.

Cement slurries which do not contain gel strength modifiers, such asthose disclosed and claimed herein, ordinarily have Zero Gel Times ofmuch less than one hour. This means that the fluid loss rate from such aslurry will still be relatively high after the slurry has reached thesecond critical value. This high fluid loss rate combined with theinability of the gelled slurry to transmit hydrostatic pressure greatlyincreases the probability that gas migration will occur.

The hydraulic cement slurry composition of this invention compriseshydraulic cement, water, present in an amount in the range of from about35 to about 60 percent water by weight of dry cement, and the polymercomposition of this invention, present in an amount in the range of fromabout 0.1 to about 2.0, preferably 0.3 to about 1.0 and still morepreferably from about 0.5 to about 0.8 percent polymer composition byweight of dry cement. Mix water concentrations greater than thosementioned can be employed in the presence of extenders and/or ultra fineand slag cements.

The slurry, in addition to the above ingredients, also preferablyincludes a high temperature set time retarder, such as sodium or calciumlignosulfonate or organic acids, such as citric, tartaric or gluconicacid, or mixtures of such acids and lignosulfonates, present in anamount in the range of from about 0.1 to about 2.0 percent retarder byweight of dry cement. Furthermore, a high temperature strengthregression aid, such as silicon dioxide, can be present in the slurry inan amount in the range of from about 0 to about 40 percent by weight ofdry cement. If desired, a weighting agent, such as hematite, may beincluded in the slurry in an amount in the range of from about 10percent to about 60 percent by weight of dry cement.

As previously mentioned, the polymer composition is a random copolymermade by reacting, in the presence of a humate, a monomer selected fromcompounds within the scope of formula (1), the vinylamide morpholinederivative, with at least one monomer selected from compounds within thescope of formula (2), the styrene sulfonic acid salt.

The vinylamide morpholine derivatives useful herein are selected fromcompounds represented by the general formula: ##STR3## wherein R₁ is --Hor --CH₃ and R₂ is --H, --CH₃ or --CH₂ CH₃ and R₂ can be positioned onany one of the four carbons in the morpholine ring.

The polymerizable styrene sulfonic acid salts useful herein are selectedfrom compounds represented by the general formula: ##STR4## wherein R₃is --H and M is --Na, --K, --NH₄, or --Ca1/2.

As previously mentioned, the polymerization reaction can also includeother acrylic derivatives such as those selected from compoundsrepresented by the general formula: ##STR5## wherein R₄ is --H or --CH₃; R₅ is --H, --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃ or --C(CH₃)₂ CH₂SO₃ X, X is --Na, --NH₄ or --Ca1/2; and R₆ is --H, --CH₃ or --CH₂ CH₃.

In one preferred embodiment, the polymer composition of this inventionconsists essentially of the random copolymerization product of thevinylamide morpholine derivative and sodium styrene sulfonate.

The mole ratio of the vinylamide morpholine derivative to the styrenesulfonic acid salt employed in the process of making the polymercomposition is an amount in the range of from about 2 to about 25,preferably from about 5 to about 20, and still more preferably fromabout 7 to about 15 moles of the vinylamide morpholine derivative permole of the styrene sulfonic acid salt. In one preferred embodiment theprocess employs about 10 moles of the vinylamide morpholine derivativeper mole of the styrene sulfonic acid salt.

The preferred vinylamide morpholine derivative is acryloylmorpholine,the preferred styrene sulfonic acid salt is sodium styrene sulfonate.

Some specific compounds within the scope of formula (1) believed to beuseful herein include acryloylmorpholine and methacryloylmorpholine.

A specific compound within the scope of formula (2) believed to beuseful herein is sodium styrene sulfonate.

Specific compounds within the scope of formula (3) believed to be usefulherein include the sodium salt of 2-acrylamido-2-methylpropanesulfonicacid, acrylamide, methacrylamide, N-methylacrylamide,N-i-propylacrylamide, N-i-propylmethacrylamide, N-t-butylacrylamide,N-t-butylmethacrylamide, N,N-dimethylacrylamide andN,N-dimethylmethacrylamide.

The polymer composition of this invention is water soluble, and can beemployed in the liquid or solid (dry) state.

The improved polymerization process of this invention can be conductedin any vessel (or series of vessels) of a size suitable to retain thevolume of the reactants. The reactor vessel can be constructed of eitherglass or stainless steel and is preferably equipped with: a means forstirring and/or circulating the contents thereof; a temperaturedetecting device and a means for recording the detected temperature;inlets for introducing liquids, solids and gasses into the interiorthereof; a pH detecting device and a means for displaying and recordingthe detected pH; and a means for heating and cooling the contents of thereactor.

In general, the improved polymerization process comprises dissolving allmonomer reactants and humate in a quantity of deionized water sufficientto dissolve the monomer reactants and humate and to cool the reaction,which is highly exothermic, followed by initiating the polymerizationreaction.

In one preferred embodiment, about 75 percent of the required deionizedwater is introduced into the reactor, the required quantity of baseneutralizer, an alkali metal hydroxide, is added to the reactor and thewater and base are mixed by stirring and/or circulation until theresulting solution of water and base is cooled to about 65° F.

The amount of deionized water added to the reactor to dissolve themonomer reactants and humate is an amount in the range of from about 3to about 4 weight parts water per 1 weight part of monomers and humate.

A preferred base neutralizer is a 50% aqueous solution of rayon gradesodium hydroxide, wherein a stoichiometric quantity of base is addeddependent on the presence of any acid monomer in the reaction mass.

Oxygen, to inhibit homopolymerization, can be introduced into thereactor containing the base solution by bubbling air into the basesolution at a rate of about 10 L/min.

Thereafter, the required quantity of any acid monomer, such as onedefined in formula (3), can be slowly added to maintain a temperaturebelow 75° F. The pH of the solution is measured to determine if the pHis in the desired range of neutral to slightly basic. Accordingly, thepH value is an amount in the range of from about 7 to about 8.5,preferably from about 7 to about 7.5, and still more preferably in therange of 7.2 to 7.3. If the pH value is less than an amount in the rangeof from about 7.2 to about 7.3, then base is added until the pH isincreased to a value within the stated range. If the pH value is greaterthan an amount in the range of 7.2 to 7.3, then additional monomer isadded until the pH decreases to a value within the stated range.

An effective quantity of humate, which is an amount in the range of fromabout 3 to about 25, preferably from about 5 to about 20 and still morepreferably from about 8 to about 13 parts by total weight of monomerreactants per 1 part by weight humate, calculated as potassium humate,is then added, with stirring, to the reactor containing the neutralizedsolution and permitted to dissolve. It is believed that the humateingredient operates to control the molecular weight of the polymercomposition wherein an increase in the concentration of humate causesthe molecular weight of the polymer composition to decrease and,conversely, a decrease in the concentration of humate causes themolecular weight of the composition to increase.

The required quantity of vinylamide morpholine derivative, such asacrylomorpholine (commonly known as ACMO), is then added to the solutionof humate and neutralized chemical in the reactor with stirring andheating. The remaining deionized water is then added to the reactor tohelp insure that all of the chemicals are in solution.

At this time the introduction of any air into the reactor is terminatedand nitrogen is then introduced into the reactor at a rate in the rangeof from about 2 to about 25 L/min to purge the reactor of oxygen.

Thereafter, the required quantity of styrene sulfonic acid salt, such assodium styrene sulfonate, is added, with stirring, at a rate to maintainthe solution at a temperature in the range of about 65 to about 75° F.

The temperature of the reactant solution is then adjusted to a value inthe range of from about 100 to about 120, preferably from about 110 toabout 114 and still more preferably to about 112° F. and maintained atthat value for a period of about one hour.

When the vinylamide morpholine derivative is dissolved and the indicateddesired temperature is obtained, then an effective quantity of a watersoluble chain transfer agent, which is an amount in the range of fromabout 200 to about 500 total moles of monomer reactants per 1 mole ofweight chain transfer agent, is added to the solution in the reactor andpermitted to dissolve therein. The chain transfer agent is preferablyadded to the reaction mass in an aqueous solution having in the range offrom about 3 to about 5 parts by weight transfer agent per 100 parts byweight aqueous solution. Examples of water soluble chain transfer agentsuseful herein include sodium allylsulfonate and tetraethylenepentaminewherein tetraethylenepentamine (commonly known as TEPA) is preferred. Asindicated, the chain transfer agent is preferably added as a 3 to 5percent aqueous solution. It is believed that the chain transfer agentoperates to control the molecular weight of the polymerization product,wherein an increase in the concentration of chain transfer agent causesthe molecular weight of the polymer composition to decrease and,conversely, a decrease in the concentration of chain transfer agentcauses the molecular weight of the composition to increase.

An effective quantity of a water soluble polymerization initiator, whichis believed to be an amount in the range of from about 70 to about 80total moles of monomer reactants per 1 mole of initiator, is added tothe reactor to cause reaction to commence. The initiator is preferablyadded to the reaction mass in an aqueous solution having in the range offrom about 15 to about 25 parts by weight initiator per 100 parts byweight aqueous solution. A preferred initiator is a 20% aqueous solutionof sodium persulfate (commonly referred to as SP). Initiators usefulherein are disclosed in U.S. Pat. No. 4,726,906.

The reaction is exothermic in nature and is accompanied by a decrease inpH of the solution. Accordingly, the temperature and pH of the reactionmass are monitored. Stabilization of temperature and pH indicatescompletion of the reaction. Typically, the pH of the solution stabilizesat a value in the range of from about 6.5 to about 7.5 and thetemperature stabilizes at a value in the range of from about 120 toabout 140° F.

After about one hour, the resulting polymerization product of theprocess is allowed to cool to room temperature.

The total weight of the disclosed vinyl derivatives, in the combinationsand mole ratios disclosed in the present application is an amount in therange of from about 10 to about 30, preferably 15 to 25 and still morepreferably from about 18 to about 22 percent by total weight ofsolution.

For purposes of comparison, a random copolymer comprising the monomerreactants employed herein can be prepared in accordance with theprocedures disclosed in copending applications Ser. No. 08/964,622,filed Nov. 5, 1997, and Ser. No. 09/092,294 filed Jun. 5, 1998.

According to the copending applications, the polymerization processcomprises forming an aqueous solution of the vinyl morpholine derivativeand a branched N-vinylamide derivative and causing the monomers to reactunder the influence of an effective amount of a suitable water solubleinitiator at atmospheric pressure and at a temperature in the range offrom about 104 to about 122 degrees Fahrenheit.

Addition of initiator to the reaction mass is conveniently effected inwater solution. For example, in one preferred embodiment featuringacryloylmorpholine and 2-acrylamido-2-methylpropanesulfonic acid as thereactants, the initiator, sodium persulfate, is added to the reactionmass in a 14.5 percent by weight aqueous solution. As such, when thecombined weights of the reactants, initiator and solution water areconsidered, sodium persulfate is present in an amount in the range offrom about 0.05 to about 0.2, preferably from about 0.075 to about 0.15and more preferably about 0.09 to about 0.12 percent by weight of theentire reaction mass.

The term "cement," as used herein, is intended to include thosecompounds of a cementitious nature which are described as hydrauliccements. Such compounds include, for example, Portland Cement in generaland particularly Portland Cements of API Classes G and H, although otherAPI classes can be utilized, as well as pozzolan cements, gypsumcements, high alumina content cements, slag cements, high gel (high claycontent) cements, silicate containing cements, ultrafine cements andhigh alkalinity cements. Portland cements and, particularly, cement ofAPI Classes G and H are preferred.

The aqueous fluid utilized in the cement composition can be water fromany source provided that it does not contain an excess of any compoundsthat affect the stability of the cement composition of the presentinvention. The aqueous fluid can contain various salts such as sodiumchloride, potassium chloride, calcium chloride and the like.

Other types of well known and conventional additives also can beincorporated into the cement composition to modify the properties of thecomposition. Such additives include additional fluid loss additives,viscosifiers, retarders, accelerators, dispersants, weight-adjustingmaterials or fillers and the like.

Additional fluid loss additives which may be incorporated into thecement composition of the present invention include cellulosederivatives such as carboxymethylhydroxyethyl cellulose, hydroxyethylcellulose, modified polysaccharides, polyacrylamides, polyaromaticsulfonates, guar gum derivatives, mixtures of such compounds and thelike. Numerous other compounds which may be utilized as additional fluidloss additives are well known by those skilled in cementing technology.

A retarder may be used in the cementing composition when the bottom holecirculating temperature exceeds 100 degrees F. Examples of retarderswhich can be used herein include lignosulfonates, such as calciumlignosulfonate and sodium lignosulfonate, organic acids, such as citricacid, tartaric acid and gluconic acid and mixtures thereof. The amountof retarder required will vary according to the bottom hole circulatingtemperatures and variation in the makeup of the cement itself.

The proper amount of retarder required in any particular case should bedetermined by running a "thickening time" test for the particularconcentration of retarder and cement composition being used. Such testsshould be run according to the procedures set forth in API SPEC 10 usinga device called a consistometer. Generally speaking, "thickening time"is defined in API SPEC 10 as the elapsed time starting when pumpingbegins and ending when the cement attains a value in the range of fromabout 70 to 100 units of consistency, referred to as Bearden units ofconsistency. Bearden units of consistency obtained on a pressurizedconsistometer are referred to as Bc units. Bearden units of consistencyobtained on an atmospheric pressure consistometer are referred to as ABcunits. In most applications the amount of retarder, if any required,will not exceed more than about 5.0 percent by weight of the dry cement.

Dispersing agents can be utilized to facilitate using lower quantitiesof water and to promote higher set cement strength. Friction reducers,which promote freer movement of the unset composition, and allow ease ofpumping through the annulus, if present, can be incorporated in theslurry in amounts up to about several percent by weight of dry cement.Some dual function additives, such as lignosulfonates, which functionboth as a dispersant and also as a set time retarder, can beincorporated in the slurry where their use would be advantageous forcertain cementing situations.

Accelerators, such as the soluble inorganic salts in addition to calciumchloride, can be utilized in amounts up to about 8 percent by weight ofdry cement.

The cement composition also may include, in particular applications,foaming agents or defoaming agents which comprise various anionic,cationic, nonionic and other surface active compounds. The amount ofsuch surface active agents added to the cement composition willtypically be in the range of from about 0.1 to about 3 percent by weightof dry cement. Generally, the selection of such additives will be withinthe skill of those knowledgeable in the art of well cementing.

Of the various types of fine aggregate which can be used, fly ash,silica flour, fine sand, diatomaceous earth, lightweight aggregate andhollow spheres can be cited as typical. The use of these materials iswell understood in the art, and so long as they are compatible with thecompositions of the invention, they can be employed over wide ranges ofconcentrations.

EXAMPLES

The following examples are provided, not by way of limitation, but toillustrate some benefits of the composition and method of the presentinvention.

Example 1

For purposes of comparison, a polymer composition, employing theingredients in the quantities set out in Table 1, below, was prepared inaccordance with the procedure disclosed in application Ser. No.08/964,622 filed Nov. 5, 1997. The reaction was conducted at atmosphericpressure and at the initial reaction temperature of 111 degreesFahrenheit. The procedure employed to make the polymer composition is asfollows.

About 70% of the indicated quantity of D.I. Water is placed in areaction vessel of suitable size which is equipped with a recirculatingpump and associated tubing, a mechanical stirrer, a nitrogen spargetube, an addition funnel, a temperature indicating means and a means forheating the vessel and the contents thereof. The mixer is activated tostir at 130 rpm and the indicated quantities of monomers are slowlyadded in sequence with continuous mixing until all monomers arecompletely dissolved. After all monomers are added, the balance of wateris added with continuous mixing. The solution is then sparged withnitrogen at 22 liters per minute for a total of 30 minutes to excludeair (oxygen) from the reaction.

Thereafter, the nitrogen sparge rate is changed to 10 liters per minute,the stirring rate is changed to 110 rpm, the entire indicated quantityof an initiator in water solution is rapidly added and the temperatureof the reaction mass is monitored until it appears to stabilize, whichis an indication of the completion of the reaction.

Thereafter, the reaction mass is recirculated until the temperature ofthe mass fully stabilizes. Then, recirculating, mixing and sparging areterminated, the temperature of the mass is adjusted to a value of about140 degrees Fahrenheit and the mass is maintained at that temperature inthe closed reaction vessel for at least about 3 hours until theviscosity of the reaction product attains a value in the range of fromabout 5000 to about 11,000 centipoises.

                  TABLE 1                                                         ______________________________________                                        PREPARATION OF POLYMER COMPOSITION ACCORDING TO                               THE PROCEDURE DISCLOSED IN                                                    APPLICATION SERIAL NUMBER 08/964,622 FILED                                    NOVEMBER 5, 1997                                                              ______________________________________                                        POLYMER A                                                                     grams                                                                                ACMO (monomer)                                                                           1406.129                                                           AMPS (monomer)                                                                           4581.259                                                           DI WATER   52162.85                                                           Sub Totals 58150.238                                                          SP (initiator)                                                                           59.00                                                              DI WATER   344.7                                                              Sub Totals 403.7                                                              Total      58553.938                                                   MOLE RATIOS                                                                          ACMO/AMPS  1/2.219                                                            MONOMERS/SP                                                                              129.49                                                      WEIGHT PERCENTS                                                                      SP (solution)                                                                            14.615                                                             SP (overall)                                                                             0.101                                                              ACTIVE     10.326                                                      ______________________________________                                         Note: 1. ACMO is acryloylmorpholine.                                          2. AMPS is 2acrylamido-2-methylpropane sulfonic acid.                         3. SP is sodium persulfate. The indicated mole ratio of SP is the sum of      the molar quantities of the monomer reactants divided by the number of        moles of SP. The indicated weight percent of SP (solution) is the             concentration of SP in the solution added to the reaction. The indicated      weight percent of SP (overall) is the concentration of SP in the entire       reaction mass.                                                                4. D.I. WATER is deionized water.                                             5. The reaction mass at this point is a liquid and has an acid pH.            6. The method of preparation of the additive, as shown in this Example 1,     produces a random arrangement of polymers.                                    7. The weight percent ACTIVE is the total weight of monomers and initiato     as a percent of the total weight of the reaction mass.                   

Example 2

Polymer A, produced as described in Example 1, above, was furthertreated by converting it from the liquid acid form to the dry salt formby base neutralization. Accordingly, Polymer A, a viscous acidic liquid,was contacted with a 30 weight percent aqueous solution of calciumhydroxide, an example of which is commercially available as MississippiLime. The pH of the solution was adjusted to a value in the range offrom about 7 to 8. Thereafter, a small quantity of a silicon solutionrelease agent was added to the neutralized solution which was thenplaced in a drum dryer rotating at 4 revolutions per minute andoperating at about 300 degrees Fahrenheit. The material was maintainedin the dryer under the mentioned conditions for a time sufficient toproduce a dried product which was then reduced to a fine powder bymilling. The milled product was then used as described in Example 3,below.

Example 3

Cement slurries were prepared and tested for fluid loss, consistency andrheological properties in accordance with the provisions of API SPEC 10.Polymer A, shown in Table 1, above, after first being neutralized, driedand milled in accordance with Example 2, was employed in the slurriesreferred to in Table 2, below. The quantities of "Polymer" and mix waterreferred to in Table 2 are expressed as percent by weight of dry APICLASS H cement unless otherwise noted.

The mix water employed, unless otherwise noted, was potable city tapwater as available in Mesquite, Texas. In some runs the mix waterincluded other ingredients which are referred to as "Additive." Thequantity of "Additive" is expressed as percent by weight of mix water.

With respect to data included in Table 2, unless otherwise noted: FluidLoss was determined in accordance with the provisions of API Spec 10,Appendix F. Consistency was determined in accordance with the provisionsof API Spec 10, Section 9. Rheological properties were determined inaccordance with the provisions of API Spec 10, Appendix H using a FannRotational Viscometer OFI Model 800 with rotor sleeve R1, bob B1 andloaded with a 1 inch spring.

                  TABLE 2                                                         ______________________________________                                        POLYMER A, FROM EXAMPLES 1 and 2 and TABLE 1                                  38 PERCENT MIX WATER                                                                    Run #                                                                         1.sup.3                                                                             2      3        4    5.sup.2                                  ______________________________________                                        Polymer, wt %                                                                             0.0     0.3    0.5    0.6  0.8                                    Additive, wt %                                                                            0.0     0.0    0.0    2.0.sup.1                                                                          0.0                                    Temp deg F. 125     125    125    125  180                                    Fluid Loss  1200    90     44     66   44                                     cc/30 mm                                                                      Consistency                                                                   initial, ABc                                                                              10      8      10     10   13                                     @ 20 min, ABc                                                                             17      9      11     9    7                                      Rheology                                                                      600 rpm     220     210    330+   330+ 209                                    300 rpm     181     124    224    161  122                                    200 rpm     159     90     165    118  89                                     100 rpm     130     53     98     70   51                                      6 rpm      21      7      12     10   5                                       3 rpm      14      6      8      7    3                                      ______________________________________                                         Footnotes Table 2:                                                            .sup.1 Calcium chloride.                                                      .sup.2 Mix water was simulated sea water, an aqueous alkaline solution        consisting of 3.4% FRITZ SUPER SALT by weight of solution. FRITZ SUPER        SALT is a concentrate available from Fritz Industries, Inc., of Mesquite,     Texas. De chlorinated water was employed to dilute the concentrate to         prepare the mix water employed in run #5.                                     .sup.3 Run #1 did not contain any polymer and is provided as a basis for      comparison.                                                              

Example 4

Cement slurries were prepared and tested for thickening time, zero geltime, transition time and compressive strength. Polymer A, shown inTable 1, above, after first being neutralized, dried and milled inaccordance with Example 2, was employed in the slurries referred to inTable 3.

The quantities of "Polymer," mix water and retarder, referred to inTable 3 are expressed as percent by weight of dry API CLASS H cementunless otherwise noted. The retarder employed, unless otherwise noted,was sodium lignosulfonate.

The mix water employed, unless otherwise noted, was potable city tapwater as available in Houston, Tex.

Unless otherwise noted, Thickening Time was determined in accordancewith the provisions of API Spec 10. Zero Gel Time and Transition Timewere determined in accordance with Sabins et al, mentioned previously,and compressive strength was measured with an Ultrasonic Cement Analyzer(UCA).

                  TABLE 3                                                         ______________________________________                                        POLYMER A, FROM EXAMPLES 1 and 2 and TABLE 1                                  MIX WATER.sup.1                                                                      Run #                                                                         6.sup.3                                                                             7       8.sup.3 9     10.sup.3                                                                            11                                   ______________________________________                                        Polymer, %                                                                             0.0     0.6     0.0   0.6   0.0   1.4                                Retarder, %                                                                            0.15    0.15    0.375 0.375 0.4.sup.2                                                                           0.4.sup.2                          Temp deg F.                                                                            140     140     200   200   250   250                                Thickening       4:45          4:20        4:19                               Time,                                                                         HRS:MIN                                                                       Zero Gel 0:53    9:05    0:47  7:13  1:07  4:01                               Time,                                                                         HRS:MIN                                                                       Transition                                                                             3:33    0:05    0:14  1:05  1:02  1:07                               Time,                                                                         HRS:MIN                                                                       Comp Strength                                                                 HRS:MIN                                                                        50 psi  8:10    9:39    7:46  10:26 5:45  6:47                               500 psi  9:35    10:51   8:27  11:18 6:31  7:44                               24 hours 2591    2786    3175  2660  2090  1439                               PSI                                                                           ______________________________________                                         Footnotes Table 3:                                                            1. Runs 6, 7, 8 and 9 were made using 40 percent mix water and runs 10 an     11 were made using 55 percent mix water.                                      2. 0.2% sodium lignosulfonate and 0.2% tartaric acid.                         3. Runs 6, 8 and 10 did not contain any polymer and are provided for          purposes of comparison.                                                  

Examples 1, 2, 3 and 4 and Tables 1, 2 and 3, above, containinformation, disclosure and data which are included in co-pendingapplication Ser. No. 08/964,622 filed Nov. 5, 1997.

Examples 5, 6, 7, and 8 and Tables 4, 5, 6 and 7, below, containinformation, disclosure and data which are included in co-pendingapplication Ser. No. 09/092,294 filed Jun. 5, 1998.

Example 5

Polymer compositions (Polymers 1, 2 and 3), employing the ingredients inthe quantities set out in Table 4, below, were prepared as follows.

The polymerization reactions were conducted in suitably sized glass andstainless steel reactors each equipped with an overhead stirrerassembly, a temperature probe connected to a recording thermometer,ports for the addition of liquids and solids, a pH probe connected to apH meter, a gas inlet tube, and a heating/cooling coil. Additionally,the stainless steel reactor was equipped with a circulation system.Polymer 1 was made in the glass reactor. Polymers 2 and 3 were made inthe stainless steel reactor.

The reactor was first charged with 75% of the required de-ionized water.The required quantity of rayon grade, sodium hydroxide (supplied as a50% solution in water) was added. The mixture was stirred and theresulting base solution was cooled to 65° F. (With regard to polymers 2and 3, the base solution was also circulated and air was bubbled intothe solution at a rate of 10 L/min.)

The required quantity of 2-acrylamido-2-methylpropanesulfonic acid(commonly known as AMPS) was measured, and then added at a rate tomaintain the solution at a temperature in the range of 65 to 75 degreesF. The pH of the solution was measured. If the pH of the solution wasbelow a pH value in the range of 7.2 to 7.3, then the sodium hydroxidesolution was added until the pH value was increased to 7.2 to 7.3. Ifthe pH of the solution was greater than 7.2 to 7.3, then additional AMPSwas added until the pH decreased to a value in the range of 7.2 to 7.3.

In the case of polymer 3, the required amount of acrylamide (AA) wasmeasured and then added to the reactor.

The required quantity of potassium humate was measured, and then addedto the reactor. Any potassium humate remaining in the measuringcontainer was washed with the reserved de-ionized water, and then addedto the reactor.

The required quantity of acrylomorpholine (commonly known as ACMO) wasmeasured, and then added to the reactor. The remaining deionized waterwas used to rinse the ACMO measuring container, and the sides of thereactor to insure the inclusion of all of the ingredients in solution.

Introduction of air into the reactor for making polymers 2 and 3 wasstopped. Nitrogen was then introduced into the reactor. (For polymer 1,the nitrogen rate was about 2 to 3 L/min, and for polymers 2 and 3 thenitrogen rate was about 20 to 25 L/min.) The solution was heated to 112°F. for a one hour.

The required quantity of a solution of tetraethylenepentamine (commonlyknown as TEPA) was added to the reactor. In the case of polymers 1 and2, a 3.0% solution was employed. A 5.0% solution was employed in makingpolymer 3.

The required quantity of a 20% solution of sodium persulfate (commonlyreferred to as SP) was added to the reactor. The pH and temperature ofthe polymerization were monitored. The pH of the solution decreased toabout 7.2 and the temperature increased to about 125 degrees F.

After about one hour, the resulting polymerization product was allowedto cool to room temperature.

Example 6

A small quantity of silicon solution, as a release agent, was added topolymers 2 and 3. These polymers were then placed in a drum dryerrotating at 4 revolutions per minute and held at a temperature of about300 degrees F. The polymers were maintained in the dryer at thementioned conditions for a time sufficient to produce a dried productwhich was then reduced to a fine powder by milling. The milled productswere then employed in the Examples 7 and 8 below.

                  TABLE 4                                                         ______________________________________                                        RECIPE FOR MAKING POLYMER PRODUCT OF INVENTION                                            POLYMER 1  POLYMER 2  POLYMER 3                                   Ingredient  Grams      Pounds     Pounds                                      ______________________________________                                        ACMO (monomer)                                                                            17.11      1.7        3.60                                        AMPS (monomer)                                                                            120.56     26.2       22.60                                       AA (monomer)                                                                              0.0        0.0        4.85                                        NaOH        23.27      5.0        8.75                                        Potassium humate                                                                          13.38      2.8        2.80                                        DI WATER    598.66     122.2      117.40                                      Sub Total   772.98     157.9      160.00                                      SP (initiator)                                                                            2.12       0.46       0.51                                        DI WATER    8.49       1.84       2.05                                        Sub Total   10.61      2.3        2.56                                        TEPA (chain transfer)                                                                     0.32       0.07       0.13                                        DI Water    10.29      2.23       2.44                                        Sub Total   10.61      2.3        2.57                                        Totals      794.2      162.5      165.13                                      MOLE RATIOS                                                                   ACMO/NaAMPS/AA                                                                            1/4.8/0.0  1/10.5/0.0 1/6.4/0.7                                   NaOH/AMPS   1/1        1/1        1/1                                         MONOMERS/SP 78.9/1     71.6/1     79.4/1                                      MONOMERS/TEPA                                                                             418.4/1    374.2/1    220.1/1                                     WEIGHT PERCENTS                                                               Potassium humate                                                                          1.68       1.72       1.74                                        SP (solution)                                                                             20.0       20.0       20.0                                        SP (overall)                                                                              0.27       0.28       0.32                                        TEPA (solution)                                                                           3.0        3.0        5.0                                         TEPA (overall)                                                                            0.04       0.04       0.08                                        ACTIVE      20.94      20.93      20.07                                       ______________________________________                                         Note                                                                          1. ACMO is acryloylmorpholine.                                                2. AMPS is 2acrylamido-2-methylpropane sulfonic acid. Prior to                polymerization, the sodium salt of AMPS (NaAMPS) is prepared by adding        NaOH to the reactor.                                                          3. AA is acrylamide. The quantity stated is 100% active, however, it is       employed as a 52% aqueous solution.                                           4. NaOH is sodium hydroxide. The quantity stated is 100% active, however      it is employed as a 50% aqueous solution to neutralize the AMPS to form       NaAMPS.                                                                       5. Humate is a generalization for any naturally occurring humic acid          derivative. The indicated weight percent of potassium humate is the           percent by weight of humate in the entire reaction mass. It is believed       that humate functions to control molecular weight of the polymer product.     6. SP is sodium persulfate, a polymerization initiator. The indicated mol     ratio of SP is the sum of the molar quantities of the monomer reactants       divided by the number of moles of SP. The indicated weight percent of SP      (solution) is the concentration of SP in the solution added to the            reaction. The indicated weight percent of SP (overall) is the                 concentration of SP in the entire reaction mass.                              7. TEPA is tetraethylenepentamine, a chain transfer agent employed to         control molecular weight of the polymer product. The indicated mole ratio     of TEPA is the sum of the molar quantities of the monomer reactants           divided by the number of moles of TEPA. The indicated weight percent of       TEPA (solution) is the concentration of TEPA in the solution added to the     reaction. The indicated weight percent of TEPA  #(overall) is the             concentration of TEPA in the entire reaction mass.                            8. D.I. WATER is deionized water.                                             9. The reaction mass at this point is a liquid having a substantially         neutral pH.                                                                   10. The method of preparation of the polymer product, as shown in this        Example 5, produces a random arrangement of copolymers.                       11. The weight percent ACTIVE is the total weight of ACMO, NaAMPS, AA,        TEPA, humate and SP as a percent of the total weight of the entire            reaction mass.                                                           

Example 7

Cement slurries were prepared and tested for fluid loss, consistency andTheological properties in accordance with the provisions of API SPEC 10.Polymers 2 and 3, shown in Table 4, above, were employed in the slurriesreferred to in Tables 5 and 6, respectively, below. The quantities of"Polymer" and mix water referred to in Tables 5 and 6 are expressed aspercent by weight of dry API CLASS H cement unless otherwise noted.

The mix water employed, unless otherwise noted, was potable city tapwater as available in Mesquite, Tex. In some runs the mix water includedother ingredients which are referred to as "Additive." The quantity of"Additive" is expressed as percent by weight of mix water.

With respect to data included in Tables 5 and 6, unless otherwise noted:Fluid Loss was determined in accordance with the provisions of API Spec10, Appendix F. Consistency was determined in accordance with theprovisions of API Spec 10, Section 9. Rheological properties weredetermined in accordance with the provisions of API Spec 10, Appendix Husing a Fann Rotational Viscometer OFI Model 800 with rotor sleeve R1,bob B1 and loaded with a 1 inch spring.

                                      TABLE 5                                     __________________________________________________________________________    POLYMER 2, FROM EXAMPLE 6 and TABLE 4                                         38 PERCENT MIX WATER                                                                  Run #                                                                         1.sup.1                                                                             12 13   14 15   16 17.sup.6                                     __________________________________________________________________________    Polymer, wt %                                                                         0.0   0.5                                                                              0.8   1.0                                                                             0.8  1.0                                                                              0.8                                          CaCl.sub.2 .sup.2, wt %                                                               0.0   0.0                                                                              0.0   0.0                                                                             0.0  0.0                                                                              0.0                                          Temp deg F.                                                                           125   125                                                                              125  125                                                                              125  125                                                                              180                                          Fluid Loss                                                                            1200  78 38    28                                                                              132  54 99                                           cc/30 min                                                                     Consistency                                                                   initial, ABc                                                                          10                                                                    @ 20 min, ABc                                                                         17                                                                    Rheology                                                                      600 rpm 220   185                                                                              227  300+                                                                             267  270                                                                              231                                          300 rpm 181   104                                                                              165  213                                                                              161  159                                                                              136                                          200 rpm 159   74 119  153                                                                              116  115                                                                              98                                           100 rpm 130   42 67    85                                                                              67   66 55                                            6 rpm  21    5  6     7 8    7  5                                             3 rpm  14    4  4     5 6    5  4                                            __________________________________________________________________________            Run #                                                                         18 19 20 21  22 23 24 25 26                                           __________________________________________________________________________    Polymer, wt %                                                                          1.0                                                                              1.0                                                                             1.0                                                                               1.0                                                                              1.0                                                                              1.0                                                                               1.0                                                                              1.0                                                                             1.0                                          NaCl.sup.2                                                                             0.0                                                                              18.0                                                                            36.0                                                                              0.0                                                                              18.0                                                                             36.0                                                                              0.0                                                                              18.0                                                                            36.0                                         Silica flour                                                                           0.0                                                                              0.0                                                                             0.0                                                                               0.0                                                                              0.0                                                                              0.0                                                                               35.0                                                                             35.0                                                                            35.0                                         Retarder.sup.3                                                                         0.0                                                                              0.0                                                                             0.0                                                                               0.2                                                                              0.2                                                                              0.2                                                                               0.5                                                                              0.5                                                                             0.5                                          Temp deg F.                                                                           180                                                                              180                                                                              180                                                                              180 180                                                                              180                                                                              180                                                                              180                                                                              180                                          Fluid Loss                                                                             52                                                                              171                                                                              169                                                                               28 74 32  22                                                                               32                                                                              24                                           cc/30 min                                                                     Consistency                                                                   initial, ABc                                                                           14                                                                               16                                                                              14  14 7  14  23                                                                               21                                             @ 20 min, ABc                                                                          11                                                                               10                                                                              8   10 6  9   15                                                                               10                                             Rheology                                                                      600 rpm 330+                                                                             330+                                                                             322                                                                              330+                                                                              257                                                                              235                                                                              330+                                                                             330+                                            300 rpm 231                                                                              204                                                                              187                                                                              191 151                                                                              136                                                                              291                                                                              230                                             200 rpm 176                                                                              152                                                                              134                                                                              134 109                                                                              96 202                                                                              164                                             100 rpm 105                                                                               94                                                                              75  72 61 53 108                                                                               88                                              6 rpm   19                                                                               22                                                                              10  6  6  5  8   7                                               3 rpm   16                                                                               20                                                                              8   5  4  4  6   5                                              __________________________________________________________________________             Run #                                                                         27 28  29 30  31 32  33 34                                           __________________________________________________________________________    Polymer, wt %                                                                           1.0                                                                             1.0 1.0                                                                              1.0 1.0                                                                              1.0  1.0                                                                              1.5                                         NaCl.sup.2                                                                              0.0                                                                             18.0                                                                              36.0                                                                             0.0 18.0                                                                             36.0                                                                               36.0                                                                             36.0                                        Silica flour                                                                            35.0                                                                            35.0                                                                              35.0                                                                             35.0                                                                              35.0                                                                             35.0                                                                               35.0                                                                             35.0                                        Retarder.sup.3                                                                          0.5                                                                             0.5 0.5                                                                              1.0 1.0                                                                              1.0  1.0                                                                              1.0                                         Temp deg F.                                                                            245                                                                              245 245                                                                              308 308                                                                              308 308                                                                              308                                          Fluid Loss                                                                              20                                                                              25  27 52  36 42   36                                                                               20                                          cc/30 min                                                                     Consistency                                                                   initial, ABc                                                                            23                   15                                                                               14                                          @ 20 min, ABc                                                                           15                   12                                                                               10                                          Rheology                                                                      600 rpm  330+                 330+                                                                             330+                                         300 rpm  291                  330+                                                                             330+                                         200 rpm  202                  224                                                                              228                                          100 rpm  108                  134                                                                              139                                           6 rpm    8                    9  10                                           3 rpm    6                    6  7                                           __________________________________________________________________________     Footnotes Table 5:                                                            1. Run #1 did not contain any polymer and is provided for purposes of         comparison.                                                                   2. Percent by weight of mix water.                                            3. Calcium lignosulfonate.                                                    4. Runs 33 and 34 contain 41.7% mix water.                                    5. Measured at 180 degrees F.                                                 6. See footnote 2, Table 2                                               

                                      TABLE 6                                     __________________________________________________________________________    POLYMER 3, FROM EXAMPLE 6 and TABLE 4                                         38 PERCENT MIX WATER                                                          __________________________________________________________________________            Run #                                                                         35 36 37  38 39 40 41  42 43                                          __________________________________________________________________________    Polymer, wt %                                                                         0.3                                                                              0.5                                                                               0.8                                                                              0.3                                                                              0.5                                                                               0.8                                                                             0.3 0.5                                                                               0.8                                        NaCl.sub.2                                                                            0.0                                                                              0.0                                                                               0.0                                                                              18.0                                                                             18.0                                                                              18.0                                                                            36.0                                                                              36.0                                                                              36.0                                       Silica flour                                                                          35.0                                                                             35.0                                                                             35.0                                                                              35.0                                                                             35.0                                                                              35.0                                                                            35.0                                                                              35.0                                                                              35.0                                       Retarder.sup.3                                                                        0.5                                                                              0.5                                                                               0.5                                                                              0.5                                                                              0.5                                                                               0.5                                                                             0.5 0.5                                                                               0.5                                        Temp deg F.                                                                           180                                                                              180                                                                              180 180                                                                              180                                                                              180                                                                              180 180                                                                              180                                         Fluid Loss                                                                            64 38  22 92 38  29                                                                              80  42  23                                         cc/30 min                                                                     Consistency                                                                           11 11  20 10 14  20                                                                              10  12  20                                         initial, ABc                                                                  @ 20 min, ABc.sup.4                                                                   9  10  14 9  10  12                                                                              9   9   11                                         Rheology                                                                      600 rpm 212                                                                              276                                                                              330+                                                                              206                                                                              255                                                                              330+                                                                             235 260                                                                              330+                                        300 rpm 112                                                                              160                                                                              315 105                                                                              131                                                                              217                                                                              115 127                                                                              196                                         200 rpm 78 113                                                                              220 71 90 154                                                                              76  90 139                                         100 rpm 40 60 121 37 47  83                                                                              41  48  76                                          6 rpm  5  5   10 4  4   7 4   5   6                                           3 rpm  4  4   5  3  3   4 3   4   4                                          __________________________________________________________________________            Run #                                                                           44    45   46    47   48                                            __________________________________________________________________________    Polymer, wt %                                                                            1.5   1.5  1.5   1.0  1.5                                          NaCl.sub.2                                                                               18.0  00.0                                                                               18.0  36.0                                                                               36.0                                         Silica flour                                                                             35.0  35.0                                                                               35.0  35.0                                                                               35.0                                         Retarder.sup.3                                                                           0.5   1.5  1.5   1.0  1.0                                          Water %    38.0  47.9                                                                               41.7  41.7                                                                               41.7                                         Temp deg F.                                                                             245   308  308   308  308                                           Fluid Loss                                                                               18    22   30    26   22                                           cc/30 min                                                                     Consistency                                                                   initial, ABc.sup.4                                                                       21    19   25    15   15                                           @ 20 min, ABc.sup.4                                                                      10    10   12    11   12                                           Rheology.sup.4                                                                600 rpm   330+  330+ 330+  330+ 330+                                          300 rpm   205   173  208   330+ 330+                                          200 rpm   146   121  146   226  231                                           100 rpm    83    65   85   137  140                                            6 rpm     7     6    7     8    12                                            3 rpm     5     3    4     5    7                                            __________________________________________________________________________     Footnotes Table 6:                                                            2. Percent by weight of mix water.                                            3. Calcium lignosulfonate.                                                    4. Measured at 180° F.                                            

Example 8

Cement slurries were prepared and tested for thickening time, zero geltime, transition time and compressive strength. Polymers 2 and 3, shownin Table 4, above, were employed in the slurries referred to in Table 7,below.

The quantities of "Polymer," mix water, accelerator and retarder,referred to in Table 7 are expressed as percent by weight of dry APICLASS H cement unless otherwise noted. The retarder employed, unlessotherwise noted, was sodium lignosulfonate. The accelerator employed,unless otherwise noted, was calcium chloride.

The mix water employed, unless otherwise noted, was potable city tapwater as available in Houston, Tex.

Unless otherwise noted, Thickening Time was determined in accordancewith the provisions of API Spec 10. Zero Gel Time and Transition Timewere determined in accordance with Sabins et al, mentioned previously,and compressive strength was measured with an Ultrasonic Cement Analyzer(UCA).

                  TABLE 7                                                         ______________________________________                                        POLYMERS 2 AND 3, FROM EXAMPLE 6 and TABLE 4                                  MIX WATER.sup.1                                                                         Run #                                                                         48    49        50      51                                          ______________________________________                                        Polymer 2, %                                                                              0.0     0.6       0.6   1.4                                       Polymer 3, %                                                                              0.6     0.0       0.0   0.0                                       Retarder, % 0.0     0.15      0.375 0.42                                      Accelerator, %                                                                            1.0     0.0       0.0   0.0                                       Temp deg F. 80      140       200   250                                       Thickening  4:05    3:45      3:45  3:39                                      Time,                                                                         HRS:MIN                                                                       Zero Gel    4:05    6:12      2:24  2:32                                      Time,                                                                         HRS:MIN                                                                       Transition  0:30    0:22      0:32  0:27                                      Time,                                                                         HRS:MIN                                                                       Comp Strength                                                                 HRS:MIN                                                                        50 psi     3:54    4:28      3:25  3:47                                      500 psi     7:50    5:50      3:59  4:35                                      24 hours    --      2669      3456  1878                                      psi                                                                           48 hours    3641    --        --    --                                        psi                                                                           ______________________________________                                         Footnotes Table 7:                                                            1. Runs 48, 49 and 50 were made using 40 percent mix water and run 51 was     made using 55 percent mix water.                                              2. 0.2% sodium lignosulfonate and 0.2% tartartic acid.                   

The polymer composition prepared by the method of the prior copendingapplication filed Nov. 5, 1997, is not the same as the polymercomposition prepared by the method of the prior copending applicationfiled Jun. 5, 1998. This difference can be illustrated by comparing thefluid loss results shown in Table 2, run 4, which employs Polymer A fromthe application filed Nov. 5, 1997, with the fluid results shown inTable 5, runs 15 and 16, which employs Polymer 2 from the applicationfiled Jun. 5, 1998. All of these runs were conducted at 125° F. andemployed the same quantity of fresh water and the same quantity ofcalcium chloride. However, the quantity of Polymer 2 required to obtainan acceptable fluid loss is greater than the quantity of Polymer A. Thedifference in the compositions can also be illustrated by comparing thefluid loss results of runs 5 and 17 and runs 2 and 12.

Example 9 Method of Making the Polymer Product of the Invention

The polymer composition of this invention, hereinafter called Polymer B,employing the ingredients in the quantities set out in Table 8, below,was prepared as follows.

The polymerization reaction was conducted in suitably sized glassreactor equipped with an overhead stirrer assembly, a temperature probeconnected to a recording thermometer, ports for the addition of liquidsand solids, a pH probe connected to a pH meter, a gas inlet tube, and aheating/cooling coil.

The reactor was first charged with 75% of the required de-ionized water.The required quantity of rayon grade, sodium hydroxide (supplied as a50% solution in water) was added. The mixture was stirred and theresulting base solution was cooled to 65° F.

The required quantity of 2-acrylamido-2-methylpropanesulfonic acid(commonly known as AMPS) was measured, and then added at a rate tomaintain the solution at a temperature in the range of 65 to 75 degreesF. The pH of the solution was measured. If the pH of the solution wasbelow a value of 7.5, then the sodium hydroxide solution was added untilthe pH value was increased to a value of 7.5. If the pH of the solutionwas greater than 7.5, then additional AMPS was added until the pHdecreased to a value of 7.5.

The required amounts of acrylamide (AA), (supplied as a 52% solution inwater) and sodium styrene sulfonate (SSS) were measured and then addedto the reactor.

The required quantity of potassium humate was measured, and then addedto the reactor. Any potassium humate remaining in the measuringcontainer was washed with the reserved de-ionized water, and then addedto the reactor.

The required quantity of acrylomorpholine (commonly known as ACMO) wasmeasured, and then added to the reactor. The remaining de-ionized waterwas used to rinse the ACMO measuring container, and the sides of thereactor to insure the inclusion of all of the ingredients in solution.

Nitrogen was then introduced into the reactor at about 2 to 3 L/min, andthe solution was heated to 112° F. for a one hour.

The required quantity of a 5.0% aqueous solution oftetraethylenepentamine (commonly known as TEPA) was added to thereactor.

The required quantity of a 20% aqueous solution of sodium persulfate(commonly referred to as SP) was added to the reactor.

The pH and temperature of the polymerization were monitored. The pH ofthe solution decreased to about 7.0 and the temperature increased toabout 130° F.

After about one hour, the resulting polymerization product was allowedto cool to room temperature.

The polymer was then dried on a hot plate for a time sufficient toproduce a dried product which was then reduced to a fine powder bymilling. The milled product was then employed in Examples 10 and 11below.

                  TABLE 8                                                         ______________________________________                                        RECIPE FOR MAKING POLYMER B                                                   ______________________________________                                        Ingredient        Grams                                                       ______________________________________                                        ACMO (monomer)    17.11                                                       AMPS (monomer)    105.51                                                      AA (monomer)      12.06                                                       SSS (monomer)     3.31                                                        NaOH              20.37                                                       Potassium humate  13.38                                                       WATER                                                                         with NaOH         20.37                                                       With AA           11.13                                                       DI water          560.92                                                      Sub Total         764.16                                                      SP (initiator)    2.46                                                        DI WATER          9.83                                                        Sub Total         12.29                                                       TEPA (chain transfer)                                                                           0.61                                                        DI Water          11.68                                                       Sub Total         12.29                                                       Totals            788.74                                                      MOLE RATIOS                                                                   ACMO/NaAMPS/AA/SSS                                                                              1/4.2/1.4/0.13                                              NaOH/AMPS         1/1                                                         MONOMERS/SP       79.1/1                                                      MONOMERS/TEPA     245.4/1                                                     WEIGHT PERCENTS                                                               Potassium humate  1.70                                                        SP (solution)     20.0                                                        SP (overall)      0.31                                                        TEPA (solution)   5.0                                                         TEPA (overall)    0.08                                                        ACTIVE            21.0                                                        ______________________________________                                         Notes for Table 8:                                                            1. ACMO is acryloylmorpholine.                                                2. AMPS is 2acrylamido-2-methylpropane sulfonic acid. Prior to                polymerization, the sodium salt of AMPS (NaAMPS) is prepared by adding        NaOH to the reactor.                                                          3. AA is acrylamide. The quantity stated is 100% active, however, it is       employed as a 52% aqueous solution.                                           4. SSS is sodium styrene sulfonate.                                           5. NaOH is sodium hydroxide. The quantity stated is 100% active, however,     it is employed as a 50% aqueous solution to neutralize the AMPS to form       NaAMPS.                                                                       6. Humate is a generalization for any naturally occurring humic acid          derivative. The indicated weight percent of potassium humate is the           percent by weight of humate in the entire reaction mass. It is believed       that humate functions to control molecular weight of the polymer product.     7. SP is sodium persulfate, a polymerization initiator. The indicated mol     ratio of SP is the sum of the molar quantities of the monomer reactants       divided by the number of moles of SP. The indicated weight percent of SP      (solution) is the concentration of SP in the solution added to the            reaction. The indicated weight percent of SP (overall) is the                 concentration of SP in the entire reaction mass.                              8. TEPA is tetraethylenepentamine, a chain transfer agent employed to         control molecular weight of the polymer product. The indicated mole ratio     of TEPA is the sum of the molar quantities of the monomer reactants           divided by the number of moles of TEPA. The indicated weight percent of       TEPA (solution) is the concentration of TEPA in the solution added to the     reaction. The indicated weight percent of TEPA (overall) is the               concentration of TEPA in the entire reaction mass.                            9. D.I. WATER is deionized water.                                             10. The reaction mass at this point is a liquid having a substantially        neutral pH.                                                                   11. The method of preparation of the polymer product, as shown in this        Example 9, produces a random arrangement of copolymers.                       12. The weight percent ACTIVE is the total weight of ACMO, NaAMPS, AA,        SSS, TEPA, humate and SP as a percent of the total weight of the entire       reaction mass.                                                           

Example 10

Cement slurries were prepared and tested for fluid loss, consistency andTheological properties in accordance with the provisions of API SPEC 10.Polymer B, shown in Table 8, above, was employed in the slurriesreferred to in Tables 9 and 10, below. The quantities of "Polymer" andmix water referred to in Tables 9 and 10 are expressed as percent byweight of dry API CLASS H cement unless otherwise noted.

The mix water employed, unless otherwise noted, was potable city tapwater as available in Mesquite, Tex. In some runs the mix water includedother ingredients which are referred to as "Additive." The quantity of"Additive" is expressed as percent by weight of mix water.

With respect to data included in Tables 9 and 10, unless otherwisenoted: Fluid Loss was determined in accordance with the provisions ofAPI Spec 10, Appendix F. Consistency was determined in accordance withthe provisions of API Spec 10, Section 9. Rheological properties weredetermined in accordance with the provisions of API Spec 10, Appendix Husing a Fann Rotational Viscometer OFI Model 800 with rotor sleeve R1,bob B1 and loaded with a 1 inch spring.

                                      TABLE 9                                     __________________________________________________________________________    POLYMER B, FROM EXAMPLE 9 and TABLE 8                                         POLYMER 2, FROM EXAMPLE 5 and TABLE 4                                         POLYMER 3, FROM EXAMPLE 5 and TABLE 4                                         __________________________________________________________________________    38 PERCENT MIX WATER (4.3 gal water/94 lb sack cement)                                Run #                                                                         52 53 54  55 56 57 58  59 60                                          __________________________________________________________________________    Polymer B, wt %                                                                        1.0       1.0      1.0                                               Polymer 2, wt %                                                                           1.0       1.0       1.0                                           Polymer 3, wt %                                                                              1.0       1.0       1.0                                        Retarder.sup.1 %                                                                       0.5                                                                              0.5                                                                              0.5                                                                               0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                               0.5                                                                              0.5                                        NaCl %   18                                                                               18                                                                               18  37                                                                               37                                                                               37                                                   Silica Flour %                                                                         35                                                                               35                                                                               35  35                                                                               35                                                                               35                                                   Temp deg F.                                                                           180                                                                              180                                                                              180 180                                                                              180                                                                              180                                                                              180 180                                                                              180                                         Fluid Loss                                                                             32                                                                               54                                                                               32  38                                                                               42                                                                               36                                                                               20  26                                                                               22                                         cc/30 min                                                                     Consistency                                                                   initial, ABc                                                                           16                                                                               10                                                                               12  17                                                                               15                                                                               16                                                                               15  17                                                                               22                                         @ 20 min, ABc                                                                          15                                                                               10                                                                               15  11                                                                               11                                                                               11                                                                               10  11                                                                               13                                         Rheology                                                                      600 rpm 300+                                                                             330+                                                                             330+                                                                              330+                                                                             330+                                                                             330+                                                                             300+                                                                              330+                                                                             330+                                        300 rpm 301                                                                              238                                                                              330+                                                                              225                                                                              207                                                                              197                                                                              243 160                                                                              266                                         200 rpm 225                                                                              175                                                                              281 152                                                                              143                                                                              134                                                                              171 110                                                                              190                                         100 rpm 143                                                                              101                                                                              177  82                                                                               77                                                                               72                                                                               95  58                                                                              108                                          6 rpm   21                                                                               9  32  5  5  5  7   4  8                                           3 rpm   15                                                                               6  24  3  3  3  4   2  4                                          __________________________________________________________________________    41.7 PERCENT MIX WATER (4.7 gal water/94 lb sack cement)                                   Run #                                                                         60 61           62                                               __________________________________________________________________________    Polymer B, wt %                                                                             1.2                                                             Polymer 2, wt % 1.2                                                           Polymer 3, wt %               1.2                                             Retarder.sup.1 %                                                                            1.0                                                                             1.0           1.0                                             NaCl %        37                                                                              37            37                                              Silica Flour %                                                                              35                                                                              35            35                                              Temp deg F.  180                                                                              180          180                                              Fluld Loss.sup.2                                                                            36                                                                              60            30                                              cc/30 min                                                                     Consistency                                                                   initial, ABc  13                                                                              10            14                                              @20 min, ABc  10                                                                              6             10                                              Rheology                                                                      600 rpm      330+                                                                             161          330+                                             300 rpm      210                                                                              84           232                                              200 rpm      151                                                                              57           165                                              100 rpm       84                                                                              31            93                                               6 rpm        6 6             8                                                3 rpm        4 5             4                                               __________________________________________________________________________     Footnotes Table 9:                                                            1. Calcium Lignosulfonate.                                                    2. Fluid loss conducted at 308° F. with top of cell at 1500 psi an     bottom ot cell at 500 psi                                                

Example 11

Cement slurries were prepared and tested for thickening time, zero geltime, transition time and compressive strength. Polymer B shown in Table8, above, was employed in the slurries referred to in Table 10, below.

The quantities of "Polymer," mix water, accelerator and retarder,referred to in Table 10 are expressed as percent by weight of dry APICLASS H cement unless otherwise noted. The retarder employed, unlessotherwise noted, was sodium lignosulfonate. The accelerator employed,unless otherwise noted, was calcium chloride.

The mix water employed, unless otherwise noted, was potable city tapwater.

Unless otherwise noted, Thickening Time was determined in accordancewith the provisions of API Spec 10. Zero Gel Time and Transition Timewere determined in accordance with Sabins et al, mentioned previously,and compressive strength was measured with an Ultrasonic Cement Analyzer(UCA).

                  TABLE 10                                                        ______________________________________                                        POLYMER B, FROM EXAMPLE 9 and TABLE 8                                         POLYMER 2, FROM EXAMPLE 8 and TABLE 7                                         40 PERCENT MIX WATER                                                                          Run #                                                                         63   64                                                       ______________________________________                                        Polymer 2, %      0.00   0.60                                                 Polymer B, %      0.60   0.00                                                 Retarder, %       0.20   0.15                                                 Accelerator, %    0.00   0.00                                                 Temp deg F.       140    140                                                  Zero Gel          4:11   6:12                                                 Time,                                                                         HRS:MIN                                                                       Transition        0:33   0:22                                                 Time,                                                                         HRS:MIN                                                                       ______________________________________                                         Footnotes Table 10: Retarder was 0.2% sodium lignosulfonate and 0.2%          tartartic acid.                                                          

What is claimed is:
 1. A method of cementing a pipe in a borehole whichpenetrates a subterranean formation, said method comprising:forming acement composition; placing said cement composition in the annulusbetween said pipe and said formation; permitting said cement compositionto set in said annulus whereby a hardened mass of cement is produced;wherein said cement composition is a slurry comprised of water,hydraulic cement and an additive made by polymerizing monomer reactantscomprised of a vinylamide morpholine derivative and a styrene sulfonicacid salt in the presence of an effective quantity of humate; whereinsaid vinylamide morpholine derivative is selected from compoundsrepresented by the first general formula ##STR6## wherein R₁ is --H or--CH₃ and R₂ is --H, --CH₃ or --CH₂ CH₃ and is positioned on any one ofthe four carbons in the morpholine ring; and said styrene sulfonic acidsalt is selected from compounds represented by the second generalformula ##STR7## wherein R₃ is --H and M is --Na, --K, --NH₄, or--Ca1/2.
 2. The method of claim 1 wherein said additive is present insaid cement composition in an amount in the range of from about 0.1 toabout 2.0 percent additive by weight of dry hydraulic cement in saidcomposition.
 3. The method of claim 2 wherein the mole ratio of saidvinylamide morpholine derivative to said styrene sulfonic acid salt insaid additive is an amount in the range of from about 2 to about 25moles of said vinylamide morpholine derivative per mole of said styrenesulfonic acid salt and the ratio of the total weight of said monomerreactants in said additive to the weight of said humate in said additiveis an amount in the range of from about 3 to about 25 parts by totalweight of said monomer reactants per 1 part by weight of said humate. 4.The method of claim 3 wherein said additive is a random copolymer ofsaid vinylamide morpholine derivative and said styrene sulfonic acidsalt.
 5. The method of claim 3 wherein said additive is a random polymerof said vinylamide morpholine derivative, said styrene sulfonic acidsalt and at least one third monomer selected from compounds representedthe third general formula ##STR8## wherein R₄ is --H or --CH₃ ; R₅ is--H, --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, or --C(CH₃)₂ CH₂ SO₃ X, Xis --Na, --NH₄, or --Ca1/2; and R₆ is --H, --CH₃ or --CH₂ CH₃.
 6. Themethod of claim 4 wherein said vinylamide morpholine derivative isacryloylmorpholine and said styrene sulfonic acid salt is sodium styrenesulfonate.
 7. The method of claim 5 wherein said vinylamide morpholinederivative is acryloylmorpholine, said styrene sulfonic acid salt issodium styrene sulfonate and said third monomer is a mixture of thesodium salt of 2-acrylamido-2-methylpropanesulfonic acid and acrylamide.8. The method of claim 3 wherein said mole ratio of said vinylamidemorpholine derivative to said styrene sulfonic acid salt in saidadditive is an amount in the range of from about 7 to about 15 moles ofsaid vinylamide morpholine derivative per mole of styrene sulfonic acidsalt.
 9. The method of claim 3 wherein said ratio of said total weightof said monomer reactants to said weight of said humate in said additiveis an amount in the range of from about 5 to about 20 parts by totalweight of said monomer reactants per 1 part by weight of said humate.